1. Field of the Invention
This invention relates to silicone oligomers useful as coupling agents for curable compositions, for instance free-radically curable filler-organic elastomeric polymer compositions having special application as insulation coatings, to compositions employing the oligomers, and to cured products obtained therefrom.
2. Description of the Prior Art
A substantial amount of research has been performed heretofore in connection with the treatment of fillers or reinforcing agents for the purpose of improving physical or mechanical properties of plastics, resins or rubbers reinforced with the filler. Much of this research has centered on the pretreatment of glass fiber reinforcement materials for resins and rubbers. For example, U.S. Pat. No. 3,702,783 describes the application as a size to glass fibers of a blend of 3-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane. U.S. Pat. No. 3,816,235 discloses a size composition for the treatment of glass fibers wherein the size composition contains a blend of aminoalkyltriethoxysilane and methyltriethoxysilane. U.S. Pat. No. 3,944,707 discloses the use as a size for glass fiber reinforcement for plastics, blends of vinyl silane or vinyl siloxanes and a beta-haloalkoxysilane. Similarly, U.S. Pat. No. 3,993,837 discloses glass fiber size compositions containing blends of epoxyalkylsilane or siloxane and a beta-haloalkoxysilane.
U.S. Pat. No. 4,049,865 discloses glass fiber size compositions containing a blend of an aminoalkylsilane and a vinyl silane. U.S. Pat. No. 4,130,677 discloses the sizing of glass bottle surfaces with an aminoalkylsilane.
Martens et al, U.S. Pat. No. 3,148,169, discloses the pretreatment of clay filler with a silicone fluid to coat the clay particles to impart a hydrophobic character to the clay and to mask the acidic nature of the clay so that peroxides later used as crosslinking agents are not deactivated.
Pickwell et al, U.S. Pat. No. 4,550,056, describes electrical cables comprising a conductor and a coating of insulation on the conductor, the coating comprising a cured composition of
(1) an organic elastomer;
(2) an inorganic filler;
(3) a coupling composition comprising (a) an ethylenically unsaturated silane, having bonded to silicon, at least one hydroxy group and/or alkoxy group; (b) a methyl ethoxy siloxane oligomer fluid; and (c) a methyl vinyl siloxane oligomer fluid.
Rykowski, U.S. Pat. No. 4,179,537, discloses blends of an organofunctional silane, e.g., vinyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes, vinyltrihalosilanes and the like with a non-organofunctional silane, e.g., alkyltrialkoxysilanes, and the incorporation of such blends into organic resins, e.g., EPDM rubber for improving the adhesion between inorganic substrates such as clay fillers and the resin. This patent fails to disclose, teach or suggest the incorporation of siloxane oligomers in the coupling composition and suggests that the presence of siloxane oligomers in the resin-filler system could have a detrimental effect on coupling efficiency (col. 4, lines 54-63).
Use of silanes having silicon-bonded 2-methoxyethoxy groups as coupling agents, e.g., vinyl-tris-(2-methoxyethoxy)silane (col. 2, lines 44-47) is also described in U.S. Pat. No. 4,179,537. Vinyl-tris-(2-methoxyethoxy)silane, has been used industrially for many years as a coupling additive in mineral-filled EPM and EPDM wire and cable insulations. EPM is an ASTM designation for copolyrners of ethylene and propylene; EPDM is a terpolymer of ethylene, propylene and a diene monomer such as ethylidene norbornene or 1,4 hexadiene. Vinyl-tris-(2-methoxyethoxy) silane has been extensively used heretofore because it provides a unique balance of elastomer reinforcement and the degree of wet electrical stability required. However, it releases 2-methoxyethanol as a hydrolysis by-product when it is used and, unfortunately, 2-methoxyethanol is now being studied as a suspected teratogen. Consequently, coupling agent products based on vinyl-tris-(2-methoxyethoxy)silane are now facing continuing replacement pressure in the marketplace.
Commercial products used as coupling agents in elastomer/filler compositions include cohydrolysis products of dimethyl and vinylmethylchlorosilanes which are used as a filler hydrophobe treatment on calcined clays. Such products however, have a relatively high cost due to the high cost of vinylmethyldichlorosilane. Reducing the vinylmethyldichlorosilane content thereof gives inferior performance in wire cable insulation applications.
U.S. Pat. No. 4,950,779, Wengrovius, et al. (General Electric), describes mixtures comprising cyclic, linear and branched alkoxy functional silicone oligomers produced by condensation of organotrialkoxysilanes, such as methyltrimethoxysilane and vinyltrimethoxysilane, using formic acid, optionally with a strong acid catalyst.
U.S. Pat. No. 5,298,998, Horn, et al. (Hxc3xcls), describes mixtures of linear and cyclic alkoxy functional silicone oligomers produced from vinyltrialkoxysilanes using hydrogen chloride catalyst and water.
U.S. Pat. No. 5,210,168, Bergstrom, et al. (Dow Corning), describes alkoxy functional silicone oligomer mixtures produced from organotrialkoxysilanes using a carboxylic acid, such as formic acid, and a strong acid catalyst.
In U.S. Pat. No. 6,140,445, incorporated herein by reference, there are described novel alkoxy functional silicone oligomers having alkoxysilylalkyl substituents on a backbone silicon atom. Such oligomers may be produced from vinylalkoxysiloxane oligomers by hydrosilation with an alkoxyhydridosilane; by hydrosilating a vinylalkoxysilane with a hydridoalkoxy silicone oligomer; or by condensation of a bis-alkoxysilane having silicon atoms joined by other than an Si-O bond, optionally with other alkoxysilanes. Such oligomers are disclosed to be useful as coatings or adhesives, or additives therefor.
The invention is an oligomer of the formula:
[R3SiOxc2xd]m[Oxc2xdSiR2Oxc2xd]n[SiO{fraction (3/2)}R]o[SiO{fraction (4/2)}]pxe2x80x83xe2x80x83(I) 
wherein
each R is selected individually from the group consisting of R1, xe2x80x94OR2 and xe2x80x94OR3; each R1 is independently a substituted or unsubstituted hydrocarbon group; each R2 is a C1-C6 alkyl group or an acyl group; and each R3 is independently an alkyl or alkenyl group having at least 8 carbon atoms;
with the provisos that
if R3 is alkenyl, there is no unsaturation within two carbon atoms adjacent to the oxygen atom of the xe2x80x94OR3 group; at least one R group is xe2x80x94OR3; at least one quarter of all R groups are xe2x80x94OR2 or xe2x80x94OR3; m=2 to 20; n=0 to 50; o=0 to 20; and p=0 to 10.
Silicone oligomers having thereon at least one C8 or higher alkoxy or alkenoxy group, preferably C10-C16 alkoxy or alkenoxy, especially dodecyloxy, have been found to hydrolyze extremely slowly. Transesterification of relatively inexpensive siliconate oligomers provides a cost effective method of providing stable silicone oligomers with lipophilic hydrocarbon functionality. While there may be some hydrolysis of the xe2x80x94OR3 groups of the oligomer over extended time periods, it does not substantially modify the overall polymer properties. Moreover, at least in the case of dodecyloxy functional oligomers, a trace level release of dodecanol can be advantageous for underground applications, such as in insulation formulations for buried cables. Dodecanol is reported as a treeing retardant in electrical insulation.
In the formula (I), above, R1 is independently a substituted or unsubstituted hydrocarbon group. For instance R1 may be a saturated or unsaturated aliphatic or aromatic hydrocarbon of 1 to 16 carbon atoms, e.g., alkyl (linear or branched), or cycloalkyl. Exemplary unsubstituted R1 groups are methyl, ethyl, 1i-propyl, 1-butyl, t-butyl, pentyl, cyclohexyl, octyl, decyl, dodecyl, phenyl, benzyl or napthyl. Methyl, ethyl and phenyl are preferred R1 groups which are unsubstituted hydrocarbon groups.
The R1 groups also may contain ethylenic or acetylenic unsaturation.
Examples of such R1 groups include vinyl, allyl, propargyl, acryloxyalkyl, methacryloxyalkyl, crotyloxyalkyl, styryl, n-octenyl, linolyl, lineoyl, etc. Vinyl, acryloxypropyl and methacryloxypropyl are preferred.
Other R1 groups may be monovalent organic radicals linked to the Si atom of the siloxane oligomer backbone by an Sixe2x80x94C bond, and which has one or more, ether, ester, carbamate, isocyanurate, thioether, polysulfide, blocked mercaptan, amide, cyano, epoxy or oximato group thereon.
Exemplary ether-containing groups include alkoxyethyl or alkoxypropyl and polyether groups, especially those obtained as a result of hydrosilation of an allyl-started poly(ethylene oxide), allyl-started polypropylene oxide or allyl-started EO/PO copolymer. Ether groups may also be provided by etherification of silylalkylhydroxides.
Exemplary ester containing groups are acetic acid, propionic acid, octanoic acid, benzoic acid, fatty acid, or acid terminated polyester, esters of hydroxyalkyl groups, for instance acetyloxypropyl, propionyloxypropyl, benzoyloxyethyl, and the like.
Exemplary carbamate containing groups may be groups obtained by reaction of silylalkylisocyanates with alcohols, and may include polyurethane as well an mono-carbamato structures. Specific such groups include propyl-N-carbamatoethyl; propyl-N-carbamatomethyl, ethyl-N-carbamatoethyl and propyl-N-carbamatoisopropyl.
Exemplary amide containing groups are suitably derived from aminoalkyl groups, amidized with a carboxylate ester such as methyl acetate, methyl propionate or a fatty acid ester, and the like. Specific such groups include 3-acetamidopropyl, 2-propionamidoethyl, 3-cocoamidopropyl.
Polysulfide encompasses groups having the functionality xe2x80x94Snxe2x80x94 therein where n is 2-8, preferably 2-4, especially disulfide and tetrasulfide. Specific such groups include: C4H9xe2x80x94SSxe2x80x94C3H6xe2x80x94 and C2H5xe2x80x94SSxe2x80x94C2H4xe2x80x94.
Blocked mercaptans are functional groups produced by reaction of a mercapto group with a subsequently removable blocking agent. Exemplary blocked mercaptan groups include thioester and other groups disclosed in copending application PCT/US98/17391, filed Aug. 21, 1998, designating US.
Representative examples of silanes which may be incorporated into the oligomers to provide blocked mercaptan groups include 3-methyldiethoxysilylpropyl thioacetate, 3-trimethoxysilylpropyl thioacetate, 3-triethoxysilylpropyl thioacetate, 3-trimethoxysilylpropyl thiopropionate, 3-triethoxysilylpropyl thiobenzoate; 3-triethoxysilylethyl thioacetate, 3-triethoxysilylmethyl thioacetate, 3-triethoxysilylpropyl thiooctanoate, and other compounds listed in PCT/US98/17391, filed Aug. 21, 1998.
Cyano containing groups are exemplified by 3-cyanopropyl.
Epoxy-containing groups are exemplified by glycidoxypropyl and xcex2-(3,4-epoxycyclohexyl)ethyl.
The R1 groups may also be substituted by a silyl group. For instance, R1 may be a group, xe2x80x94Axe2x80x94W, which comprises a silyl group W and a divalent linking group A which is attached by an Sixe2x80x94C bonds to group W and to a silicon atom of the siloxane oligomer. Preferably such a group is internal (i e. non-terminal) to the oligomer. The divalent linking group A creates a non-siloxane bridge between the siloxane oligomer and the silyl group W. The linking group A may contain hetero atoms in the structure so long as Sixe2x80x94C bonds are used at the ends of the linking group to form the respective connections the oligomer and to the silyl group W. The linking group may be linear, branched or cyclic and may be olefinically or aromatically unsaturated. The linking group may be, for instance, alkylene, alkarylalkylene or alkarylene, or it may be alkylene which is interrupted by hetero-atom containing organic structures such as ether, including polyether; ester, including polyester; carbamate, including polyurethane; isocyanurate; thioether; polysulfide, including disulfide and tetrasulfide; or the like. Preferably the linking group is an alkylene of 2 to 12 carbon atoms. The linking group A may be substituted with silyl or siloxy functions, as well as unsaturated groups. Indeed, group A may form part of a backbone with relatively linear siloxane chains attached to either end of the group. Examples of linking groups A include cycloaliphatic groups such as 1,4-diethylenecyclohexylene: 
or 1,3,-diethylene-5-triethoxysilylethylcyclohexylene: 
branched or linear aliphatic groups such as ethylene, 1,2-propylene, 1,3-propylene, 1,4-butylene, 1,3-butylene, 1,2-butylene or 2,2-dimethyl-1,3-propylene; arylene groups such as 1,4-phenylene; alkarylalkylene groups such as 1,4-diethylenephenylene: 
divalent polyether groups of the formula:
xe2x80x94CrH2rxe2x80x94(OCsH2s)qxe2x80x94
where q is 1-50, preferably 1-5; r and s are integers of 2-6; and divalent thioether or polysulfide-containing groups of the formula:
xe2x80x94CtH2txe2x80x94Suxe2x80x94CtH2txe2x80x94
where t is 2-16, preferably 2-4, and u is 1-8, preferably 2-4. Preferably the linking group is an alkylene of 2 to 12 carbon atoms, more preferably 2-3 carbon atoms.
The silyl functional group W in the structure xe2x80x94AW may be a silyl group having hydrolyzable functionality, such as alkoxy or acetoxy functionality. Alternatively, the group W may be a silicon linked organosiloxane or polyorganosiloxane group. Preferably, the silyl group W is an alkoxysilyl group or a further siloxane oligomer of alkoxy silane monomers, more preferably a dialkoxysilyl and most preferably a trialkoxysilyl group.
A preferred group xe2x80x94Axe2x80x94W may be represented as xe2x80x94CfH2fxe2x80x94SiR1g(X)3-g wherein the structure xe2x80x94CfH2fxe2x80x94 corresponds to A and the structure xe2x80x94SiR2g(X)3-g corresponds to W. Suitably, f=2 to 12, g=0 to 2, X is a hydrolyzable group such as halogen, oxime, alkoxy, aryloxy, alkenoxy or acetoxy and R1 is as previously defined. More preferably f=2 to 6, g=0-1, X is methoxy, ethoxy or acetoxy, and R1 is methyl. Exemplary such groups are xe2x80x94C2H4Si(OCH3)3; xe2x80x94C2H4Si(OC2H5)3; xe2x80x94C2H4Si(OCH3)2(CH3); xe2x80x94C2H4Si(OCH3)2Cl; xe2x80x94C2H4(C6H9)(C2H4Si(OCH3)3)2; xe2x80x94C2H4(C5H8)C2H4Si(OC2H5)3; and xe2x80x94C2H4Si(OCH3)2(OSi(OCH3)3).
R2 is a C1-C6 alkyl group or an acyl group. Exemplary R2 groups are methyl, ethyl, 1i-propyl, n-propyl, 1-butyl, t-butyl, pentyl, cyclohexyl, octyl, acetyl, benzoyl and propionyl. Preferably R2 is lower alkyl (C1-C6), more preferably methyl or ethyl.
R3 is a C8 or higher alkyl or alkenyl group. Examples include octyl, nonyl, decyl, dodecyl and alkyl groups derived from fatty acids, which may be saturated or unsaturated, for instance myristyl, palmityl, stearyl, palmitoleyl, oleyl, linoleyl, and mixtures such as coco alkyl, tallow alkyl, etc. Preferred R3 groups are C10-C16 saturated hydrocarbon groups, especially dodecyl.
Preferably m+n+o+p less than 50, more preferably xe2x89xa645, even more preferably  less than 30 and most preferably  less than 15. In its broadest aspect, m=2 to 20, n=0 to 50, o=0 to 20 and p=0 to 10. Preferably, m=2 to 10, n=0 to 20, o=0 to 20 and p=0 to 10. More preferably m=2 to 10, n=0 to 20, o=0 to 10 and p=0 to 5. Even more preferably m is 2 to 4, n is to 1 to 15, o is 0 to 2 and p is 0 to 1, though it is understood there may be distributions of the number of siloxy units within a given oligomer batch. This preference will also depend on the oligomer structure itself. It should also be noted from the foregoing that while linear structures are among the even more preferred structures, linearity is not necessary. The preferred, more preferred and even more preferred structures may also include branched structures.
Preferably there are multiple xe2x80x94OR2 groups available on the oligomer so that upon curing these oligomers may cross-link with each other and/or the inorganic filler, if present. Thus, R is xe2x80x94OR2, more preferably ethoxy or methoxy, in at least one quarter of the R groups, while the remainder of the R groups are R1 or xe2x80x94OR3 groups. More preferably at least half of the R groups are xe2x80x94OR2 or xe2x80x94OR3 groups. Also preferably, with respect to the individual M (terminal) or D (linear) units of the oligomer, if one R is R1 it is preferred that the other R group or groups on such unit are xe2x80x94OR2 and/or xe2x80x94OR3.
It is preferred that the oligomer has a viscosity of 0.5 to 500 csks or more preferably 0.5 to 200 csks (25xc2x0 C.). As is clear to one of skill in the art, the viscosity of the oligomer may be adjusted by adjusting the number of siloxy groups in the oligomer. In most applications the viscosity will be adjusted for a specific application to ensure that the composition containing the oligomer will spread over a specific substrate or be sprayable.
Oligomer Manufacture
The oligomers may be formed by condensation reactions of one or more silane compounds having an average of 2 or more xe2x80x94OR2 groups per molecule, in a manner such that at least one xe2x80x94OR2 group remains on the oligomer, and then fully or partially transesterifying the oligomer xe2x80x94OR2 groups with a C8 or higher alcohol. The individual silane compounds used to prepare the oligomers have at least one alkoxy group or acyloxy group, but preferably are di- or tri-alkoxy silanes.
The condensation may be performed according to any of the procedures disclosed in the previously identified patents, U.S. Pat. No. 4,950,779, Wengrovius, et al., U.S. Pat. No. 5,298,998, Horn, et al., U.S. Pat. No. 5,210,168, Bergstrom, et al., and in U.S. Pat. No. 6,323,277 and WO Application No. PCT/US99/08533, all of which documents are incorporated herein by reference.
Representative examples of alkoxysilanes which may be used in the condensation reaction include: vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinyltriisopropenoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, acryloxypropyltriethoxysilane, acryloxyethyltrimethoxysilane, trimethoxysilylpropyl methyl maleate, styryloxypropyltriethoxysilane, allyltrimethoxysilane, allyloxypropyltriethoxysilane, allyl-N-(3-trimethoxysilylpropyl)carbamate, methacrylamidopropyltriethoxysilane, methacryloxypropyleneoxypropylmethyldimethoxysilane, crotyloxypropyltrimethoxysilane, 1,4-bis-(triethoxysilylethyl)cyclohexane; 1,3,5-tris-(triethoxysilylethyl)cyclohexane; bis-(triethoxysilylethyl)benzene; tris-triethoxysilylethyl isocyanurate, 1,4-bis-(triethoxysilyl)butane, phenyltrimethoxysilane, phenylmethyldimethoxysilane, napthyltrimethoxysilane, cyanopropyltriethoxysilane, glycidoxypropyltriethoxysilane, beta-(3,4-epoxycyclohexyl)trimethoxysilane, (polyethyleneoxy)propyltrimethoxysilane, (poly(ethyleneoxy)(propyleneoxy))propyltriethoxysilane, 3-trimethoxysilylpropyl acetate, 3-methyldiethoxysilylpropyl acetate, phenyl N-(3-trimethoxysilylpropyl)carbamate, 3-triethoxysilylpropyl N-phenylcarbamate, methyl N-(3-trimethoxysilylpropyl)carbamate, 3-methyldiethoxysilylpropyl thioacetate, 3-trimethoxysilylpropyl thioacetate, 3-triethoxysilylpropyl thioacetate, 3-trimethoxysilylpropyl thiopropionate, 3-triethoxysilylpropyl thiobenzoate; 3-triethoxysilylethyl thioacetate, 3-triethoxysilylmethyl thioacetate, 3-triethoxysilylpropyl thiooctanoate, and the like. Corresponding compounds in which silylalkoxy groups are replaced by silyloxyacetyl groups may also be used.
Moreover, in the condensation, dialkoxysiloxy units may be inserted into the oligomer to affect the cross-linking, surface active and viscoelastic properties of the oligomer. This may be done by using tetraalkoxysilanes, such as tetramethoxysilane or tetraethoxysilane.
The condensation of the alkoxy silane monomers is suitably performed in the presence of a carboxylic acid (e.g., acetic or formic acid) or water. Alternatively, a strong condensation catalyst may be used, e.g., a strong acid or an acidic ion exchange resin such as AMBERLYST resin from Rohm and Haas Co. The other reaction conditions of the condensation will depend on the monomeric silanes; however, temperature ordinarily will be in the range of 20 to 60xc2x0 C.
The oligomers of the invention are useful as crosslinkers, coupling agents, adhesion promoters, as intermediates for the preparation of other oligomers and as filler treating agents. Illustrative compositions into which the oligomers may be incorporated include curable polymer/filler compositions used for wire and cable insulation and the like; silicate hard coats; adhesion promoting primers for paints or adhesives; masonry sealants; UV or EB cured acrylic coatings; (meth)acrylate ester based adhesives and sealants, such as anaerobic adhesives and polymer-in-monomer syrup adhesives; polyester resin systems used to form reinforced composites with fiberglass, carbon or kevlar reinforcements; and RTV silicones.
The oligomers may also be converted to hydrolyzates, in which the OR2 groups are replaced by OH, and used in that form in aqueous dispersions, as adhesion promoting or sealing primers, as additives to polymer emulsions, as filler treating agents and in curable silicone formulations.
Curable Polymer/Filler Compositions
Curable polymer/filler compositions of the present invention may comprise: (1) a free-radically curable organic polymer, (2) an inorganic filler and (3) an oligomer of the invention. The composition may also include a free-radical catalyst or generator. Typical organic polymers to which the present invention applies are curable elastomers such as any of the synthetic or natural rubbers with which fillers are conventionally employed. Examples include natural rubber, synthetic rubbers such as styrene-butadiene rubber, ethylene-propylene copolymers, polyethylene, ethylene-vinyl acetate copolymers, ethylene-propylene terpolymer rubbers in which the third monomeric component is ethylidene norbornene or 1,4-hexadiene, urethane rubbers, polyisobutadiene rubbers, and any other vulcanizable or crosslinkable elastomeric material.
The inorganic fillers which may be used in the curable compositions are known to those skilled in the art and include any suitable finely divided or particulate inorganic substance. At the time of incorporation into the curable composition most fillers may be in the form of finely divided particles. They may be approximately isometric, having a maximum diameter, i.e., a maximum linear dimension of ten xcexcm, preferably five xcexcm; or they may be in the form of plates or needles (fibers) having a thickness or diameter of twenty pm or less, preferably five pm or less. Compositions containing larger particles may be usefully formulated, but they tend to give poor properties. The minimum size of the filler particles is not critical, any of the conventionally used fillers being suitable in this respect. Among the specific fillers which may be used in the present invention are asbestos, ground glass, kaolin and other clay minerals, silica, calcium silicate, calcium carbonate (whiting), magnesium oxide, barium carbonate, barium sulfate (barytes), metal fibers and powders, glass fibers, refractory fibers, titanium dioxide, mica, talc, chopped glass, alumina, aluminatrihydrate, quartz, wollastonite (calcium silicate), and inorganic coloring pigments. Kaolin clay is a filler of choice in the wire and cable industry and therefore is preferred.
A heat activated free-radical catalyst or generator will typically be incorporated into the curable compositions of the invention. However, in some cases such a catalyst may not be required, for instance when the oligomer contains disulfide or polysulfide groups, or when other sources of free radicals are used such as UV radiation. When a free-radical catalyst is employed it may be any known catalyst or vulcanizing agent compound, of which organic peroxides, azonitrile compounds (e.g. AIBN) and sulfur are examples. Metal drier compounds, such as fatty acid, octoate or naphthoate salts of zinc, calcium, cobalt, copper, molybdenum, manganese, chromium or nickel, may also be used as cure catalysts. Preferred catalysts are organic peroxides. Any of the peroxides described or listed in Martens"" U.S. Pat. No. 3,148,169 can be employed. The catalyst is one which is heat activated so that when a mixture of the organic elastomer and catalyst is heated to a given temperature or temperature range the crosslinking reaction takes place.
Any other additives conventionally employed in free-radically curable polymer/filler to the curable composition can be used. For example, stabilizers and antioxidants, cure boosters, cure activators, cure accelerators, crosslinkers, waxes, oils, wet electrical stabilizers, and plasticizers can be added. Additional pigmentation can be provided and any other additive for providing or modifying other properties can be used. Other silane crosslinkers, such as vinyltrimethoxysilane or (meth)acryloxytrimethoxysilane, may also be included in the composition, or such silanes may incorporated into the organic polymer backbone by copolymerization.
The proportions of components in the curable composition are not narrowly critical and conventionally are based on weight parts per 100 wt. parts of organic elastomer. On this basis the inorganic filler can be varied from 25 to 200, preferably 50 to 150, wt. parts per 100 wt. parts of elastomer. The coupling composition can be present in an amount ranging from 0.1 to 10, preferably from 0.5 to 3 weight parts per 100 wt. parts of filler and the peroxide or other radical catalyst can be used in amounts of 0.5 to 10 wt. parts, preferably 2 to 5 wt. parts per 100 wt. parts of elastomer.
The curable compositions, except for the catalyst component are conventionally prepared in a BANBURY mixer (Farrel Co.) or any other intensive mixer. Accepted rubber industry compounding techniques may be used. The catalyst, if employed, may be added in the BANBURY mixer or by transferring the resulting compound to a roll mill wherein it is rolled and the peroxide is added and mixed into the compound. Either way, the result is a curable composition which then can be used to coat electrical conductors for the purpose of insulating same after curing. These compositions can also be used for a variety of other applications where low water pickup is desirable, for instance encapsulating of electrical components and other electrical insulation applications, gaskets, seals, pump diaphragms, automotive ignition wires, sulfur cured rubbers, etc. Wire and cable insulations are preferred uses for the filled compositions of the invention.
In order to cure the curable compositions it is only necessary to apply heat above the temperature at which the catalyst becomes activated. Preferably a peroxide is chosen for use having a decomposition temperature in excess of 200xc2x0 F. (93xc2x0 C.), preferably in excess of 250xc2x0 F. (121xc2x0 C.). In producing insulated wire cable the curable composition, in heated readily deformable condition (but below the decomposition temperature of the catalyst), is applied through an extruder to a conductor to form an insulating coating around the conductor. After extrusion onto the conductor the combined conductor and coating of curable composition is passed into an oven or autoclave where the temperature is raised to a point above the decomposition temperature of the peroxide upon which the curable composition crosslinks to form a tough cured thermoset insulating coating around the conductor.
Other Curable Compositions
These oligomers of formula (1) above, are also useful in coatings or adhesive formulations, as crosslinkers, adhesion promoters, to provide a dual radical/moisture cure mechanism, and/or to provide moisture resistance in the cured coating. The oligomers may be used as reactive diluents, in that they have little volatility, provide little or no contribution to volatile organic compounds (VOCs) and have an adjustable viscosity to match an application, or to dilute another composition to make the entire composition spreadable or sprayable. For such applications oligomers in which R3 comprises an acrylate or methacrylate group are preferred.
The oligomers may be used in masonry waterproofing, paints, corrosion protection systems, and on substrates such as cement, metal, polymers (PVC, PVS, EPDM, PE, PP, ABS, EPR, BR, silicone, polycarbonate, etc.), wood, a paint layer (as a primer) or rubber. Moreover, oligomers may be used in silicate hardcoats.
The oligomers may also be employed in curable compositions comprising ethylenically unsaturated monomers or prepolymers and a free-radical catalyst. Such compositions include UV or EB curable adhesives and coatings, resins and gel-coats formulated from unsaturated polyesters, anaerobically curable adhesives, acrylic engineering adhesives based on polymer-in-monomer syrups, and the like. For such applications the oligomer preferably comprises a free-radically curable group, for instance one or more R3 groups, or vulcanizable group, such as a blocked mercaptan or polysulfide. More preferably the oligomer comprises at least one vinyl, acryl or methacryl group. The oligomer may be employed at levels of from about 0.5 to about 99% of such compositions, preferably about 1 to about 50%, depending on the properties desired to be obtained or modified in the cured formulations.
The adhesive and coating compositions of the invention also will typically include a free-radical catalyst, although this is not always necessary, for instance in formulations designed for EB curing or where the oligomer contains a polysulfide group in the bridge group B or in an R4 group. The free radical catalyst may be any of the heat activatable catalysts described above or a free radical photoinitiator. Examples of free-radical photoinitiators include benzophenone, acetophenone, chlorinated acetophenone, dialkoxyacetophenones, dialkylhydroxyacetophenones, dialkylhydroxyacetophenone esters, benzoin, benzoin acetate, benzoin alkyl ethers, dimethoxybenzoin, dibenzylketone, benzoylcyclohexanol and other aromatic ketones, acyloxime esters, acylphosphine oxides, acylphosphosphonates, ketosulfides, dibenzoyldisulphides, diphenyldithiocarbonate and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide. Typically the photoinitiator will be employed in an amount of 0.1 to 10%, preferably 0.5 to 5% by weight of the composition.
The adhesive or coating compositions of the invention may also include any other component conventional for the type of formulation into which the oligomer is incorporated.
The invention is illustrated by the following examples.